Problem: $ E = \left[\begin{array}{rrr}1 & 1 & 1 \\ 2 & 2 & 1 \\ 1 & 0 & 0\end{array}\right]$ What is $ E^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}0 & 0 & 1 \\ -1 & 1 & -1 \\ 2 & -1 & 0\end{array}\right]$